1. Field of the invention
This invention relates to an optical-card reader and to an apparatus and method for reproducing data from selected tracks of an optical card. The term "optical card," is used herein to mean a card on which data can be recorded and reproduced optically, or one on which data can be recorded and reproduced photomagnetically.
2. Description of the Prior Art
FIG. 6 shows a known optical card 40 and includes an enlarged portion showing data tracks, on which data are recorded and reproduced optically by a card reader/writer. Optical card 40 has a data recording area 41, within which a number of tracks 43 are separated from each other by track guides 42. Data are recorded on tracks 43 in the form of pits 44. In general, optical cards typically have a recording capacity of around two megabytes.
Since the number of data which can be recorded on a single track of the card is limited, it is not unusual for a large data set to be recorded on several tracks or even on several tens of tracks. Thus data must be recorded and reproduced continuously over a number of tracks.
The recording of data on an optical card entails a number of coding operations, including error detection prior to recording, error correction and data interleave. To read the data from the card, then, it must first be decoded, and only one data track can be decoded at a time.
To continuously regenerate a large data set which ranges over a number of tracks, decoding from a track must begin while the data are still being read from the track. The data in the subsequent track cannot be read until the decoding of the previous track has been completed.
FIGS. 7 and 8 show the timing of the card-feed operations in relation to the read and decode operations in an existing device for recording and reproducing data on optical cards.
FIG. 7 shows the timing which exists after the card is conveyed back to its starting point. Data will be read only while the card is being fed forward (forward conveyance). The optical card is conveyed forwardly by the feed device in the direction in which its tracks are oriented (Direction X in FIG. 6). The optical head which reads the data off the card is conveyed in the direction Orthogonal to that of the card's movement (Direction Y in FIG. 6), to access the specified track.
As shown in FIG. 7, the optical card is conveyed in a forward direction when a read command is output by the CPU. As the card is being conveyed forward, the data are read from the specified track by the optical head. As soon as all the data have been read from the first track, the decoding operation is begun. While decoding is in process, the optical card is then conveyed in the reverse direction. The amount of time it takes to reverse is determined by how fast the card-feed device conveys the marginal portion of card 40 which surrounds recording area 41 and how long it takes for the conveyor motor of the card-feed device to come to a halt and start up in reverse.
When decoding has been completed for the data on a given track, the newly decoded data are transmitted to the CPU as a response. If data are being continuously reproduced over a number of tracks, a read command for the next track will be transmitted by the CPU as soon it receives the response. However, at this moment the card feed device is in the midst of conveying the card in the reverse direction. Therefore, before the reading of the data on the next track can begin, there is an unavoidable wait (waiting time) while the reverse feed of the card is completed and the direction of feed is changed.
FIG. 8 shows the timing relationship between the card-feed and the various operations when the card is fed in two directions and the data are read off the card during both forward movement (forward conveyance) and reverse movement (reverse conveyance).
As shown in FIG. 8, the optical card is conveyed in a forward direction when a read command is output by the CPU. As the card is conveyed forward, the data are read from a first specified track by the optical head. As soon as all the data have been read from the first track, the decoding operation is begun. While decoding is in process, the card-feed operation will be halted after the direction of card-feed has been reversed, and will remain stopped (stop time) until a read command for the next track is issued by the CPU.
When decoding has been completed for the data on a given track, the newly decoded data are transmitted to the CPU as a response. If data are being continuously reproduced over a number of tracks, a read command for the next track will be transmitted by the CPU as soon as the response is received. This command will cause the optical card to be conveyed in the reverse direction and its data to be read and decoded exactly as before.
As has been discussed above, the following problems occur in existing recording and reproducing devices for optical cards when data which extend over a number of tracks are to be continuously reproduced. When the data are read while the optical card is being fed forward (FIG. 7), a waiting time is required between the decoding of one track's data and the reading of the next track's data while the card-feed device starts up its forward operation.
When the data are read while the optical card is being fed both forward and in reverse (FIG. 8), the card-feed operation must be halted during the time that a single track's data are being decoded.